His point is simple: a congressperson generally need focus only on their state or district's polling, and even then it is when they are approaching a re-election campaign. Meanwhile, a President has to be concerned with national polling numbers all the time, and all potential swing-state polling approaching a re-election (that is, the other side will vote against him very likely and his side will very likely vote for him).
Someone like Trump is a bit of a special case, because his campaign and governance style is to pointedly appeal to a very specific set of people. He has done nothing to try to expand his support in office, so it is absolutely crucial for him to keep that base (while, I suppose, praying the Dems run another Hillary in 2020, with just as inept a campaign as she).
These facts inform the poll-reader as to which polls matter when, to whom, and how much. Yes, it matters that Pelosi is looking better, but that sort of polling rather matters more for the next Presidential campaign, not her own re-election campaign. (She's essentially got a safe seat, no?).