http://elderscrollsonline.com/en/media/screenshots/337
i dont know if its true maybe it is the way they cast their flames magic
for me its quite cool although does TES lore agrees with this?

I assume you're asking if this is a retcon, as if it's in TESO, it's going to be part of TES lore.

But Daedroth in TES4 would sometimes shoot fireballs from their mouths, so it's already been established.

No rules say that magic can only come from the hands, there are stranger areas to use magic from... Looking at you Vivec.

I just realized something: If Molag Bal was the Dreughs' version of Auriel in a previous kalpa (Bal the Tyrant, Auriel the King), the fire-breathing thing, plus their general appearance, makes me wonder about any possible relationship between Daedroth and dragons.

I don't understand why they don't have a proper name because "daedroth" is just the singular form of "daedra". Why did they do that?

Quoth Ted Peterson:
"There is a creature simply called a Daedroth, after all: those big, bipedal, reptilian beasts that are the terror of the four corners of Tamriel. Somehow, in ages past, they were given this confusing name, probably by someone who, when asked what that creature was, gave a generic answer which was taken to be a specific one.

This isn't as stange as it seems. If you look up the origin of just about any word, it evolves from the general to the particular. It has come to time in Tamriel where no one, except for a few snooty academics, would say "Daedroth"."

I believe they made use of fire based attacks before (In the form of Oblivion and Morrowinds fireball of course), so I really don't see a problem with this. It just looks more like a 'natural' attack as opposed to than a garden variety spell.

That is a very good point. It can't be a coincidence. While this kalpa has dragons flying around destroying things, the last kalpa would have likely had Daedroth swimming about doing the same. That would mean the Daedroth's mouth-based magic is the Thu'um, or something that precedes Thu'um. The roars we hear must be some type of language.