I believe your second guess is correct. There are two versions of the same photo--one smaller one to display in the forum, and the link takes the reader to the original larger version. Thanks for sharing, Bob.
There's no harm in Bob's responding to a direct question about how he posted a thumbnail link. I don't think it was meant personally. While your pictures are large in dimensions, the file size is generally small, which is nice.
There's just a balance to consider with a wide variety of users from across the planet. Not all users have high bandwidth, not all users have studio monitors running on 2560x1600. Much like our gear choices, those who are mindful of web design and ease of use also appreciate the results of a more 'lightweight' approach.