Pine (パイン) is likely a contraction of pineapple (パイナップル), as the Japanese word for pine is matsu (松=まつ) and I don't think many Japanese are familiar with the English word for it.
Just FYI, Thumbnailator itself doesn't delegate processing to native processing -- it's just a wrapper around Java's Image I/O[1] functionality. In other words, it delegates the compression/decompression to loaded Image I/O plugins, hence, whether native processes are used depends on those plugins.
In terms of cross-platform support, the default Image I/O plugins that come with Java shouldn't be much of a concern. For 3rd party ones, IIRC there are some that will use native libraries, while others are pure Java. One good library on the Image I/O plugins front is TwelveMonkeys ImageIO[2], which provides plugins to support a wide variety of image formats.