In my books it's an SM1, plain and simple. Why not ask the guys you're referring to as to why they call it an SM2?

I think the only SM model that was ever labelled (on the machine) as such was the SM2 - and even then only one the earlier models. The SM2 had the same ribbon cover and case shape as the subsequent SM3, 4, and 5 models.

The SM1 was an early post-war offering by Olympia that was very similar to the models that it offered before and during the war such as the Progress (below). Optima's first post-war effort was also a version of the same machine called the Elite (often referred to as the Elite 1), which wasn't really original given the Elite name was used by Olympia before/during the war .

1937 Progress



1949 SM1


'50s SM2

 

For what it's worth, the SM1 was only produced between 1949 and 1951, whereas the SM2 started production in 1950 and ran concurrent with the SM3 as the more basic portable in Olympia's model range. I had a look at the blog you linked to, and the serial numbers mentioned in it fall within the range of the SM1's serial numbers, which spanned 12,301 to 135,086. SM2 serial numbers started at 80,000 and ran into the millions. My SM1 (pictured in my previous post) has a serial number of 16,486.