Ext4dist latency shorter than biolatency

Hi, I am trying to measure latency of a read() call at two levels, ie from virtual file system layer and from block io layer. I am using bcc tools ext4dist (measured from when the operation was issued from the VFS interface to the file system, to when it completed) and biolatency (time was issuing a request to the device, to when it completes) tools. I cleared all disk caches before triggering both the tools. The results don't make sense to me. One would expect ext4dist's latency to be longer than biolatency's latency. But that is not the case. Am I missing something here?
Latency at the FS layer:
````
Tracing ext4 operation latency... Hit Ctrl-C to end.
^C

operation = read
usecs : count distribution
0 -> 1 : 3 |****************************************|
2 -> 3 : 2 |************************** |
4 -> 7 : 2 |************************** |
````
Latency at the block io layer:
````
disk = 'nvme0n1'
usecs : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 98 | |
32 -> 63 : 164318 |****************************************|
64 -> 127 : 40329 |********* |
128 -> 255 : 82992 |******************** |
256 -> 511 : 9 | |
512 -> 1023 : 0 | |
1024 -> 2047 : 1 | |
2048 -> 4095 : 20 | |
````