This is very likely to be correct.
If the Lions go 3-1 and the Eagles go 4-0, they'd both be 15-2, but the Lions would have the one-seed via tiebreaker based on conference record (if the Lions loss is to the Bills), or very likely based on strength of victory (if the Lions loss is to the Bears, 49ers, or Vikings). The Lions are currently at an NFC best 0.510 in that mark, while Philly is at 0.400. I'm not doing the math, but I doubt they can catch up even if we lost to the Vikings (which would improve that mark the most).
If the Lions go 3-1 and the Vikings go 4-0, they'd both be 15-2, but the Lions would have the one-seed and division based on record against common opponents, because the Vikings lost to the Rams.
If the Lions go 3-1 and both the Eagles and Vikings go 4-0, all three would be 15-2, but my understanding (though I am not positive) is that the divisional tie is determined first, then the postseason seeding tie. Which means that the Lions would win the tiebreaker against the Vikings, then win the tiebreaker against the Eagles, and that there would be no three-way tiebreaker to determine the one-seed.
Credit to @lordstanley for doing a lot of this work earlier in the thread.