Not true.
UPDATE: Richard Baehr has informed me that, while Rudy’s statement about the number of mail-in ballots was fascinating, it was also incorrect.
A Florida professor meticulously tracked the early mail-in voting in Pennsylvania. including the number of absentee ballots requested and the number returned, all while noting party registration. and county. Richard says, “I tracked this every day and the numbers requested and received were both over 2.5 million. This information is on the Pennsylvania state election website and the professor’s. I have no idea where Rudy gets his numbers, but they are wrong.”
Following your link, and then a link from that page to another one, which was the original UNOFFICIAL source, is the underlying information:
https://electproject.github.io/Early-Vote-2020G/PA.html#mail-ballots-rejected
There, you do see that more than 1.8M mail in ballots were supposedly sent out, possibly closer to 2.5M total, to both parties.
However, it does show that only mail in ballots were returned by Democrats.
Maybe the terms are being crossed up. Maybe Rudy meant that only ~1.7M mail in ballots were returned by Democrats, but there is a tally somewhere that shows how many total mail in ballots were for each candidate, and there are 2.4M that are shown for Biden, which would be roughly equivalent to ALL mail in ballots.
Just guesses, obviously. Most importantly, that site is not an official site, nor an official record.