Really? seems massively implausible.
They're both looking at the polls during different periods of the campaign, mostly before the party conventions.
In June, before the conventions and before he dropped out, Perot led Bush by ~8% while Clinton had less than 25% of the vote.
In July, after Perot's bizarre behavior and the DNC convention, Clinton polled at 55%.
Late in September, after Perot's reentry and the RNC convention in August, Clinton's polls steadily dropped down towards the 43% he received in November.
Perot's campaign, especially his dropping out and reentering, managed to both hurt and help both Bush and Clinton at different times. Before he dropped out, he was taking more of the "we want change/reform" vote away from Clinton than he was taking the "steady on/fiscal responsibility" vote away for Bush. After he dropped out, the "change/reform" went almost exclusively to Clinton giving Clinton the biggest convention boost in history.
The convention boost is what allowed Clinton to win, he lost ~12% of his lead between June and November, so Perot did help Clinton. It was more a matter of giving Clinton enough momentum to last 100 days or so than a matter of taking enough votes away from Bush.