Weird Science

Science geeks... I mean, "astronomers" have recently received a signal they think could be coming from outside our universe. Some suggest this may be the strongest evidence that there is life outside our planet. My favorite part of this article is the following:

Named SHGb02+14a, the possible alien communication has a frequency of about 1420 megahertz - one of the main frequencies at which hydrogen, the most common element in the universe, readily absorbs and emits energy. Some astronomers have suggested that aliens trying to announce their presence would be likely to transmit at this frequency, and SETI researchers regularly scan this part of the radio spectrum.

How exactly do these astronomers know which method the aliens prefer for to use for contact? Logical deduction based on other known aspects of alien behavior?