Well the probability is going to be hard to calculate given we only one universe in our test group, the first obvious flaws in his claim were: Can he demonstrate that the characteristics that have to remain “vanishingly small”, for the carbon based based life we observe to have exist, could be otherwise? Or that it is impossible for any other forms of life, to emerge if they were different? He could do neither of course, so his claims of improbability wee entirely subjective.
When I said that his claim that “life emerging was fortuitous” is a subjective claim, I mean for example, the mergence of life came with ubiquitous suffering, and mass extinctions. So whether we find the notion fortuitous doesn’t seem like an objective claim to me. As one could argue either way.
The rest of his spiel was predicated on different forms of argumentum ad ignorantiam fallacies. Insisting someone prove the universe could only be caused by natural phenomena, or it must have been designed by a deity using supernatural powers.
It went on in that vein for some time, until he ended up losing it, and hurling insults around, before storming off.