This doesn’t affect the argument. It’s equally compatible with the leading alternative hypothesis: that young seals start with no aversion to killer whales, but acquire an aversion to seal-eating whales by observing them eat mammals similar to their own size.

This is irrelevant. There’s no indication harbor seals use the behavior of fish to distinguish between seal-eating and fish-eating killer whales.

This strengthens the marine biologists’ hypothesis that young seals start with an aversion to all killer whales. It casts doubt on the leading alternative hypothesis: that young seals start with no aversion to killer whales, but learn to be afraid of the seal-eating ones.

If anything, this makes the leading alternative hypothesis more likely. Since it means young seals start with no aversion to other predator species, it suggests the marine biologists’ hypothesis—that young seals start with an aversion to killer whales—would be an anomaly.

If anything, this makes the leading alternative hypothesis more likely. It implies harbor seals at least sometimes learn to pick out the chattering of dangerous killer whales and acquire an aversion to those whales.