You've got the returns for the doge wrong. It has fallen in value.
Yes it has 85% of its value. so is fallen for like 20%
The problem is you can't easily correlate these price changes to the BTC halving. People have known about this for some time prior and to an extent this was factored a bit into the price. Additionally, there have been a number of pumps and market lead fluctuations as already noted.
As a result, sorry to say, but I don't think your figures show anything meaningful.
Bitcoin halving is an meaningful date. Many sold their alts to hold BTC since expected BTC will go up. I actually think is most meaningful date of all but 3 months is just short period of time, so all price changes coins had show way to much. I will do same at new year, it will look more clear.