What I gathered from colleagues who had similar issues (and who also successfully fixed it using an oven), the soldering or something else tends to crystallise and form thin threads, eventually causing a subtle short circuit that b0rks your laptop. 170 degrees may not be enough for flow soldering, but it should be enough to melt those threads / crystals down and break the short.
The temperature is just on ok for reflow, but the board temperature wasn't ramped to the normal reflow curve. Stresses can cause problems as well, so he's certainly on the winning side of things that could go wrong. That indicates to me that the assembly quality is pretty good to begin with.
