Sorry, I was in a hurry (lunch was waiting ).
Okay, let's expand a bit.
Interesting what scripple found.
The URL I posted above, obviously refers to Elk 1.1 that has mainly 1 little difference: the use of some more html5 tags in probably more appropriate positions.
To be on the same line, I tested also an 1.0 site:
https://www.google.com/search?q=%22Adesso%20metto%20una%20seconda%20immagine,%20ma%20prima%20un%20po%27%20di%20testo%20per%20fare%20spazio%20e%20vedere%20quanto%20taglia.%22
and this, again, is interesting, even more because it's a direct (involuntary) comparison with an SMF 2.0 site.
So, what we see is:
1) the topic of the elk site is apparently not indexed,
2) instead the profile page is indexed,
3) the SMF site shows the topic.
Since scripple mentioned classes, let's see the chain we have in the three situations:
1) elk display page:
html
body#chrome.action_messageindex.board_1
div#wrapper.wrapper
div#main_content_section
div#forumposts.forumposts
form#quickModForm
div.post_wrapper.windowbg
div.postarea
div#msg4.inner
2) elk profile page:
html
body#chrome.action_profile
div#wrapper.wrapper
div#main_content_section
div#admin_content
div#profilecenter
div.windowbg.core_posts
div.inner
3) SMF 2.0 (PremiumMGC theme)
html
body
div#wrapper
div#content_section
div
div#main_content_section
table#sp_main
tbody
tr
td#sp_center
div#forumposts
form#quickModForm
div.windowbg
div.post_wrapper
div.postarea
div.post
div#msg_15026.inner
For the sake of comparison, elk 1.1 has:
html
body#chrom.action_messageindex.board_3
div#wrapper.wrapper
section#main_content_section
div#forumposts
main
form#quickModForm
article.post_wrapper.forumposts
div.postarea
div#msg_28413.inner
What scripple is suggesting could make sense, the only two potential post-related identifiers in 1.0 are:
div.post_wrapper.windowbg
div.postarea
though, both contain the word "post", but is not the full name of the class, it's part of a bigger name.
So it could mean that google doesn't "split" the class name, but just takes everything and compares it with some list of words that may mean "content".