is it? the attiny85 is still marketed as being arduino compatible, but with only 6 i/o pins, it is nothing like any other arduino product.

They appear to mean compatible with breadboards (i.e. you can attach pins to it with standard spacing), not some sort of hardware form factor similarity.

"Arduino compatible" refers to the structure of the pins for external accessory hardware, but not for actual microcontrollers, which is what this is.

They also clarify a bit farther that they are, in fact, referring to software compatibility:

    ARDUINO COMPATIBLE

    NavSpark is designed to run Wiring, the same simple code as the Arduino platform. There is no need to learn any new programming language or environment. Your standard Arduino sketches run on NavSpark.