I think the guy was saying that you have to surround an expression with ‘log()’ to get the logarithm—which is inconvenient when it's a result of previous calculations and you have to shuffle the cursor around. Can't just slap ‘log’ and have the current expressions logarithmized.

However, seeing as the calculator allows writing expressions with multiple operations, just shoving everything on the screen into ‘log()’ would be unreasonable, as one might want to provide the exact place for the logarithm themselves—so I guess the app does the most reasonable thing it can.