Strength alone doesn't make you throw faster. If that was the case you would have bodybuilders out there throwing 125.
It's a matter of having strength in the correct muscles, and the technique to maximize that strength. If you follow the pitching "industry", you will see how new analysis and research leads to improvements in these areas on a regular basis.
Although there are exceptions from any generation, today's pitchers on average are bigger and stronger than in the past. It should be no surprise to see they also throw harder.
There are definitely small guys who are capable of throwing with high velocity. Although I think you will find those small guys still possess a large amount of "functional" strength, and typically are very mechanically efficient.
My son is on the small side for a pitcher at 5'10, 180lbs. However he possesses great strength in his arms and shoulders. He out arm-wrestled everyone on his team this season, including guys with 3-4 inches and 50 lbs on him. He also throws about 5 mph harder than any of them. I definitely see a correlation there.