The fuse settings of lfuse 0x62 hfuse 0xDF efuse 0xFF are the factory default settings for the Attiny85 MCUs. It sets it up so the default clock is the 8Mhz internal clock, with prescaling of 8, making the system clock speed 1Mhz. No low voltage (brownout) detection, does not allow the Attiny to reprogram itself, and leaves the external reset enabled.
The settings that the digispark uses (lfuse 0xE1 hfuse 0x5D efuse 0xFE) instead instructs the Attiny85 to use the PLL clock (nominally 16Mhz) with no default prescaling (so it really will be 16Mhz system clock). The brown-out detection is turned on (as recommended when using the PLL) and set to trigger at approximately 2.7v. The external reset is disabled (allowing use of the reset pin as an I/O). And self-programming is enabled.
The brown-out detector prevents the Attiny85 from getting stuck in an endless reboot loop if the supply voltage drops down below the trigger voltage - it keeps the Attiny85 in a reset state until the voltage rises sufficiently. Self-programming is how the micronucleus 'bootloader' is able to reprogram the Attiny85, and even update itself.