I see nothing wrong with this speculation, from a US point of view: A wave of Mexican climate refugees from Mexico City could fuel the Republican propaganda machine tar Biden as being soft on the border, and help Trump. Even though sadly Republicans in the Senate are blocking a bipartisan Senate border security bill.
Although Mexico is having a presidential election too, which makes the statement somewhat ambiguous, although Mexico's election day is really soon on June 2nd, which is well before summer.