............................................................................................................................................................................

Yes .. it was user error.
There were a number of problems with your piloting.
1.  You just sent your Phantom up 300 metres without any consideration for conditions up there
2.  You initiated RTH and observed your Phantom going backwards at 4.75 m/sec for almost a minute .. that's a bit of a clue that it was battling a strong headwind
3.  You left your Phantom up there @300m and did nothing to bring it down where it might have been able to deal with the headwind
4.  Although you had lost signal from the Phantom, your Phantom still had control signal but you didn't realise this and did nothing for 5 minutes, letting your Phantom drift further backwards although it was in RTH

Your suggestion that a WU wind report from Arlington Municipal Airport is comparable to the conditions you flew in, is not valid.
WU gives one figure for the wind speed for the whole day and one direction.
During the day the wind comes and goes - it's not static - but you think this one number is somehow magically a reliable figure to compare with the true speed and direction at the place and time you flew?
How far from where you were flying was the airport weather site
What time was the reported wind?
How much does the wind at the location you flew, at the time and at the height you flew differ from the official weather station?
How reliable is your attempt to translate the WU report to the altitude your P3 was at?  I suspect it's highly dubious.

HealthyDrones wind isn't necessarily going to be perfect at showing the exact wind - but it gives a reasonable idea.  The direction indicated by HD is confirmed by the drift you saw.
The drift recorded would suggest that the wind speed was at least 3 m/s faster than RTH (10 m/s).

You're lucky to still have your drone.
I wonder if you learned anything and how much longer you'll be flying it.

Why do you think that pilots receive the windspeed and direction at different altitudes ...

Also, wind is usually (though not always) a lot stronger after 100m up but also changes direction a due to coriolis effect and less friction. Careful preparation is everything.

Why start a second thread?
Trying to blame Healthy drones makes no sense.

I have always found them to be accurate. Check the entire flight log from take off and see where the changes occur. At least you live to fly another day and don't let criticism bother you. All of us have been there and things still can go wrong when we least expect it. With time you will become a good pilot. Practise "ATTI" mode in a nice clear open area to hone your skills and build up your confidence. Knowledge and practise are a wonderful thing when things go wrong.

There is a reason flight plans always include altitude, and it isn't just to avoid a 747

Whatever calculation you did is irrelevant.  The weather forecasters use calculations based on very complicated models through very expensive computers & they get it wrong on a daily basis.  There are too many variables to be accurate.  There can be several layes of air moving in different directions, at different speeds & at different altitudes.

You should think yourself lucky the wind wasn't blowing in the opposite direction, considering you were flying at 300m, less than 3 miles from Arlington airport!
You should probably read this.