it is both.
the same old people have gained a lot of money from previous altcoin pump and dumps. for example those who started participating in the altcoin pump and dump game with 1BTC could have had 10BTC in a short time last year during the same pumping season. so now they are again coming back in with the previous profit + some more money out of their pocket since last time it was successful.
also obviously bitcoin growth and all the adoption and all the media coverage has attracted a lot of new people. many of which are investing only. and when they get familiar with bitcoin they also find out about another market which is rising at the moment they found out about bitcoin. so without knowing they invest in altcoins too. and many end up losing a lot because they don't know what the pump and dump games in altcoins are.
Do you think there is some stats website supporting this? Some site showing how much money is flowing into BTC and alts...