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It’s not really an argument. They’ve played similarly difficult schedules. Purdue has a slightly better scoring differential, thus, a gap.
What OAM is slightly overlooking is he’s placing modest value on the order of these things, which is usually overstated. The gap between those two teams is 0.44 points. So the Boiliers would be a half-point favorite in a neutral field by this metric. And I don’t know that is that much of a reach.
Now there’s two interesting elements to this. For one, we probably understate the impact of schedule on record, granted we treat schedule as one flowing number, which is often not super helpful. It also opens the door for a Mid-Major to hammer its schedule with such ferocity it gets nice and high here. Which I don’t mind, but does irk some.
In the end, I’m not really for treating rankings as power rankings. I’m not for using poll logic either.

Sometimes the bloody-minded universe has one back go in when the OL is blocking best and one go in when it's blocking worst. You'd think such things would always be 50/50. But last year with Evans and Higdon at Michigan, I noticed that they definitely aren't always like that. And if you can put up 100 yards with clearly inferior blocking, that'd be another way to rank higher than your teammate on PFF, despite that other guy having even more yards.

But if Purdue beats Ohio State, no one is going to say it means Purdue is better than Ohio State.

The most important thing for predictive value is how well a team plays, not whether it won or lost.  When Purdue was 0-3, we all saw them as a dangerous team capable of upsetting someone later in the year.  0-3, but "impressive losses" that indicated potential.