try:
which bitcoind
echo $PATH
You'll probably find that it's picking up the bitcoind from /usr/local/bin instead of running the "bitcoind" in the local directory. If you want to override the "path"... use ./ notation to indicate you wish to run from the local dir (or provide the full path to the executable)...
For instance, from your "~/Downloads/bitcoin-sv-1.0.0.beta/src" directory
./bitcoind
or, from anywhere
~/Downloads/bitcoin-sv-1.0.0.beta/src/bitcoind
Assuming there is actually a "bitcoind" in your "~/Downloads/bitcoin-sv-1.0.0.beta/src/" directory
running ./bitcoind in that directory does start a service in top called bitcoin-main (i'm sure related to SV); but it automatically shuts off for some reason even though Core is not running. any ideas?