I had a look at that site. I can see where the confusion is coming from.
They have renamed the 3 IR bands as IR1 IR2 and IR3.

I downloaded each band from that sample data and did some basic false colour combinations. What I saw was that a [IR3, IR1, Green] false colour combination corresponded to a ETM742 image.

In common remote sensing the landsat bands are refered to Band 1 through to Band 7 and Panchromatic. The normal band descriptions can be seen here in the Official Landsat 7 Documentation. Look at Table 1.2
http://ltpwww.gsfc.nasa.gov/IAS/handbook/handbook_htmls/chapter1/chapter1.html

Looking at the link below, you can see a table showing the correct band names again and their radiometric characteristics.
http://glcf.umiacs.umd.edu/data/guide/technical/landsat.shtml

Band 5 and 7 are Mid Infra Red (These correspond to the confusing IR2 and IR3)
Band 6 is Termal (In ETM it's split into 2, so it corresponds to ThL and ThH)
Band 4 is Near InfraRed. (This corresponds to IR1)

The thing about Earth temperature is, it's emittive.
Mid-IR is reflective.
Only the Far-IR (Thermal) is emittive.
http://www.ccrs.nrcan.gc.ca/ccrs/learn/tutorials/fundam/chapter1/chapter1_3_e.html

http://imagers.gsfc.nasa.gov/ems/infrared.html

This means that what you display as IR3 is infact Landsat ETM Band 7.

What you really need for the Earth Surface Temperature is Landsat ETM Band 6 (Or ThL/ThH on the site you listed)

Click Here for a sample image of ThL that I contrast stretched.
You can see the sea is black, cold relative to the land.
The land a pale grey warm relative to the sea and cool relative to other features.
Some of the buildings stand out, almost white, much warmer compared to the surrounding land.