Your presumption are totally right because most cryptocurrency holder and investors usually sell some portion of their coins when it this season but doesn't mean the whole downtrend happened all because of that.
you should never make assumptions just because price made a certain movements. if you look back at the previous 10 years only some of the years price dropped and the rest of the time price has been rising.
so unless YOU yourself have sold bitcoin to buy gifts you shouldn't assume others are doing it.