I'm torn between two ideas concerning this picture. One is what was discussed previously -that titans are people who've some way came back from death, and that's way that guy and titan share the big bushy beard. However, their faces aren't alike, and we don't have much proof that this random guy has become a kyojin.
The other one is a bit silly, but I wanted to know whatya think about it. What if titan's aren't so dumb and they actually shave their facial hair? That would explain how the bearded titan is the only one with beard.
The bearded guy and Titan looked even more similar in the Manga. It's not the only case either where Titans with unique plot relevance look like people who had recently died/been missing.
I don't know if you're up to date with the Manga or not? If not then this would be a spoiler
Longer beard makes sense if gramps survived a couple months before becomming titan snack.