1.3 - does Roon sometimes play back from memory?

I was just looking at my network usage with version 1.3 and noticed something strange. Most of the time when playing music I notice the send and receive network data is consistent when looking at Task Manager. If I am playing a redbook PCM file, my Roonserver pc first receives a spike of data at 50mbps then settles into receiving data at 4-5mbps and sends data at 8-10mbps in short little bursts. This results in a nice, consistent, sawtooth type of pattern for the send and receive data throughout the duration of the song until about 10 seconds remaining when no more data is received.

Sometimes see a different behavior though that makes me wonder if Roon is playing the music back entirely from memory. I see the same send data pattern throughout the song but sometimes the receive data increases to 50mbps for a while (usually less than 20 seconds for redbook pcm) then drops to zero for the duration of the song instead of staying at the consistent 4-5mbps pattern like before. I am assuming that during the 50mbps spike, Roon is downloading the entire song and playing back from memory instead of downloading little chunks at a time like it usually does?

So my questions are:
Is Roon indeed playiing back from memory?
If so, why doesnt Roon always play back from memory?