The two uses are unrelated and both common. A grinding tape moves a little at a time with no clean entries, frustrating to trade and often the prelude to a larger move. A trader who is grinding is making modest repeatable profits rather than chasing large ones.
The second sense is the one worth adopting. Most durable trading records are built from unremarkable repetition, and the desire for a single large result is usually what interrupts it.
Related: crab-market, patience, process-goals, printing