Problem with AES-128 AddRoundkey Step
You are not missing anything, the calculation is wrong. The calculation of the key schedule that is.

If you postulate the round calculations are correct, the round keys must be wrong, and in fact that byte of the round key is indeed wrong. Reversing the AddRoundKey calculation from the round example, the valid round key byte resulting in 0x77 is 0x87, not 0xB7.

Therefore the slide was just wrong, the values may have been entered by hand, and 8 looks like a B, so that is very likely.