It should be true but it's not all of the pumpers will be pumping the coin with good fundamentals. Sometimes the whales are randomly pumping the undervalued coin.
The problem is how do you know about that? So many people are speculating about this but again the pump can't be predicted but you can try to follow the fundamental of coin-like what news that will come soon and this can attract the whale to pump it.
I have been making a lot of money by following the rumour and news about some altcoins.