This kind of files is usually used for speed tests, the files simply contain some random garbage and are large enough to allow for a speed test without to much fluctuation:
[timwolla@~]wget -O /dev/null http://195.88.75.46/payload/20MB.bin
--2014-03-23 01:47:40-- http://195.88.75.46/payload/20MB.bin
Connecting to 195.88.75.46:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 20971520 (20M) [application/octet-stream]
Saving to: ‘/dev/null’
100%[======================================>] 20,971,520 671KB/s in 33s
2014-03-23 01:48:13 (615 KB/s) - ‘/dev/null’ saved [20971520/20971520]
/dev/null
is used as the output file to reduce the performance penalty introduced by the hard disk.
So: This is nothing specific to lighttpd, but the lighttpd is probably used to reduce the load on the machine as it performs pretty good when serving static files (at least it performs better than the Apache2).
Here are other examples of such pages, with similarly named files: