There was certainly gross ignorance in this presentation to say that Baptists do not believe in the Trinity.
But probably the fact underneath this is that *some* Baptists and other evangelicals do not baptize thrice in the name of the Father, Son, and Holy Spirit, but rather baptize once in the name of Jesus.
There had probably been examples at that parish where some baptisms from Baptists had not been accepted for that reason, and the person doing the tour made the incorrect assumption that this meant there was not a belief in the Holy Trinity.
Really? You must have visited some very strange Baptist and "other evangelical" churches. I haven't been in or heard of any that didn't follow Matthew 28:19: "Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit"
Regretfully, I would guess that you have the same problem that the Orthodox guide had. That is, you heard rumors from others and believed them without investigating. You really need to learn more about non-Orthodox Christianity before blindly believing what an ignorant person tells you.