Lr always uses three decimals for dimensions in the export dialog. So 22 cm is exactly the same as 22,000 cm.
Maybe you're used to a dot as a decimal separator, and a comma as a thousand separator? If so, it probably looks like 22 thousand cm to you.
Whether to use a dot or a comma for a decimal separator, is set in your computer's operating system.
On windows, Control panel > Region and language.
The above is correct but my system uses decimal point . as expected. Mac 10.10.2 L2 5.7.1...
I don't think I have heard of Lightroom using a comma as a decimal separator at all...
It depends on the language settings in the OS.
My OS and Lightroom are in English, but under Region and language in the control panel (Win 7), Format is set to Norwegian.
This means that decimal points, date formats, time formats, etc. are displayed Norwegian style in all applications, so my LR uses a comma as decimal separator.
Interesting that the OP would have a comma as he is Australian......