You didn't say for how long the temp stayed at 150, but I'm going to hazard a guess that the wind rushed through a gap, splashed on the temp probe and that gave the low reading. Given the ~10cfm flow rate of these pellet grill combustion fans and the size of the cook volume, I suspect the cool inside breeze was flushed out the exhaust within 5-10 seconds and the temperature returned to normal. Am I close?
If you had only a few of these excursions during a mult-hour cook, it would truly be a negligible effect. Note the heat capacity of meat is far greater than that of air so even if the air dropped 50 degrees for a few seconds, I'm sure the surface temperature of the meat (to say nothing of the bulk) didn't change by more than a degree due to that. And if you pull your meat based on meat temperature (suggested) instead of time-in-smoker, this is more a nuisance than a true problem.
But heck, I don't like nuisances...
Rotating the unit by 90 degrees may help, or hanging a damp tee-shirt over the offending gap should do the trick. (A full blanket would deflect the wind too, but that's kind of overkill for just a wind problem.) Leaning a half sheet of plywood up against the unit would give you a shield effect too. (You do need to determine the wind direction so your plywood is perpendicular to it and upstream from the smoker. But like Bob Dylan says, you don't need a weatherman to know which way the wind blows.)
Hanging a 20# weight on the door handle can help close up gaps too. If that's too Mickey Mouse for you, a lot of people put toggle clamps to help push the door shut in a the gap-piest areas. Of course that's 2 added latch actions to do each time you open the door...it'd drive me crazy.