In the last bull season in 2017, after bitcoin got high to $17k - $19,000 , many investors decided investing in altcoins and that caused them to bull and I think that is what is also happening now. Etheruem is no longer what it was last year, bnb, cardano, litecoin, even doge coin all have increased. So I think the bull for altcoins is already happening. Check your portfolio and you can see some difference in there.
^ Because the fact that as of now altcoin was depends on the dominance of BTC and you are right, we are already in altcoin season.
I did not see any sign that when BTC was down altcoin will up, BTC and ETH are almost the same have terrible fees, they are the leading coins and I think the opposition movement against them will not happen. Probably those who increase more than 50% were in manipulation altcoins, it most likely they are on pump and dump. Nevertheless, this is my perception, we still don't know what will happen next.