I've heard that Korean people can not cross the Thai border since 13th march 2014 by land from Thailand?

Are you talking about citizens from North or South Korea?

As far as I know South Korean passport holders are stamped in for 90 days.

Are you asking about entering Thailand?

If so, wrong forum.

Or are you asking about leaving Thailand and entering a neighbouring country?

If so, which country(ies)?

I mean, south-Korea people can not leave from Thailand to all countries by land just now. Is that correct?

Where have you got that from?

I mean, south-Korea people can not leave from Thailand to all countries by land just now. Is that correct?

Why would Thailand prevent someone with a properly issued passport and valid permission to stay in Thailand, etc from leaving the country by whatever route they chose?

Very strange!

Yes but No but Yes but --------

Maybe the kimchi is fermented too much? I asked my Korean students this and they all laughed.

To,get back on topic I am not aware of any directive or rule to support claims made by the OP.

It is apparently a unfounded rumor or a misunderstanding.

The misunderstanding or misinformation could be that somebody was informed on entry after doing a number of border crossings for a new entry that they would get no more after the one they were doing. They do limit those at many border crossings now.